PROBLEM: Reduced Engine Power and Service Active Handling - Z06Vette.com

GR8 WHITE · 07-05-2009, 07:14 PM

All, I was at the car wash rinsing off the engine bay. Something I do on a monthly basis. When I started up, about 3 seconds later the REDUCED ENGINE POWER came on along with SERVICE ACTIVE HANDLING.

#1. Are these two code normally hand in hand?

#2. If so, will a bad throttle body, position sensor, or connector wire cause the Service Active Handling, or is it more reverse that "Service Active Handling" will induce the Reduced Engine Power code to protect the car?

No matter how much I cleared the codes, the codes always came back. I removed the throttle body (right side) connecter, blew it out, let it air dry, checked for kinked wires etc. Removed teh air bridge and checked the throttle body blade. It is unobstructed.

Joe (JOPHIS37) came over and double checked all areas. Disconnected the battery, sat for 5 - 7 minutes, reset the codes, started up and did an idle re-learn. It seemed to work initially and then shut off after 1 minute or so going back into Reduced Engine Power. We reset the codes, started up again and let it idle re-learn. Car ran for 15 minutes at idle, no issues. No codes.

Got on the road to head home. Took it easy. Low RPMS, low MPH. No issues, but didn't want to push it. 500 feet from home, I punched it to see what would happen.

Car fluttered as if it were starving for fuel, started to backfire (pop) more than I ever heard it do and went back into Reduced Engine Power.

Codes have been consistent:

PCM:
P1120 TP Sensor 1 Circuit
P1220 TP Sensor 2 Circuit
P1221 TP Sensors 1, 2 Performance
P1516 Command vs Actual Throttle Position Performance (TAC Module)

TCS:
C1278 TCS Temporarily Inhibited By PCM

HVAC:
B0338 Inside Air Temp Sensor Open
B0361 Left Actuator Feedback Short to GND
B0441 Left Actuator Out of Range
B0446 Right Actuator Out of Range
P1518 PCM to TAC Module Serial Data Circuit

One thing that has me puzzled is, the front end has been rattling a bit more lately. While getting my fuel filter changed, I noticed that when I push up and down on my front sway bar, the adjustable end links seem to be clicking. They are tight, but maybe worn out?

Is there anything in the front end to check for traction control connectors?
When I drive over bumps, something is rattling like it is loose. At first, I thought it was my wheels. I am sure it is suspension related, but are these two problems connected somehow?

Could a faulty fuel filter have any suspicion in this scenario? It worked perfectly fine for 400 miles up to Phoenix and back. Only after I washed teh car did it start this madness.

Ideas, suggestions?

RocketSled · 07-05-2009, 07:58 PM

Man... I vote for water. Note the comment below on "water intrusion".

DTC P1516

Circuit Description

The predicted throttle position, based on the accelerator pedal position and possibly on other limiting factors, is compared to the actual throttle position. The 2 values should be within a calibrated range of each other. Both the powertrain control module (PCM) and the throttle actuator control (TAC) module redundantly monitor the predicted and the actual throttle position. This DTC sets if the TAC detects an out of range condition between the predicted and the actual throttle position.

Conditions for Setting the DTC

The TAC module detects that the predicted and actual throttle positions are not within a calibrated range of each other.
OR The PCM and the TAC cannot determine throttle position.
OR Both throttle position (TP) sensors are invalid
All of the above conditions are met for less than 1 second.

Action Taken When the DTC Sets

The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
The control module commands the TAC system to operate in the Reduced Engine Power mode.
A message center or an indicator displays Reduced Engine Power.
Under certain conditions the control module commands the engine OFF.

Conditions for Clearing the MIL/DTC

The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

Inspect the TAC module connectors for signs of water intrusion. When water intrusion occurs, multiple DTCs could be set with no DTC circuit or component conditions found during diagnostic testing.
Ensure that the starting and charging systems are operating properly. Low system voltage can cause this DTC to set.
When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.

For an intermittent, refer to Intermittent Conditions .

RocketSled · 07-05-2009, 08:00 PM

And...

DTC C1278

Circuit Description

The EBCM and the PCM simultaneously control the traction control. The PCM reduces the amount of torque supplied to the drive wheels by retarding spark timing and selectively turning off fuel injectors. The EBCM actively applies the brakes to the front wheels in order to reduce torque.

The EBCM sends a requested torque message via a pulse width modulated (PWM) signal to the PCM. The duty cycle of the signal is used to determine how much engine torque the EBCM is requesting the PCM to deliver. Normal values are between 10 and 90 percent duty cycle. The signal should be at 90 percent when traction control is not active and at lower values during traction control activations. The PCM supplies a pull up voltage of 5 volts that the EBCM switches to ground to create the signal.

The PCM sends a delivered torque message via a pulse width modulated (PWM) signal to the EBCM. The duty cycle of the signal is used to determine how much engine torque the PCM is delivering. Normal values are between 10 and 90 percent duty cycle. The signal should be at low values (around 10 percent) at idle and higher values under driving conditions. The EBCM supplies a pull up voltage of 12 volts that the PCM switches to ground to create the signal.

When certain PCM DTCs are set, the PCM will not be able to perform the torque reduction portion of traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.

RocketSled · 07-05-2009, 08:01 PM

The PCM knows it can't control the throttle reliably, and that's what's setting the Service AH/TC message.

At a guess, I'd say you've gotten water *inside* the TP Sensor itself, it's not a "wet connector" problem. Odds are, having managed to get the motor nice and hot on your drive home, and having sat overnight, it'll be fine in the morning once that moisture "cooks off".

GR8 WHITE · 07-05-2009, 08:06 PM

Rocket, if perhaps you are correct, where is this Throttle Position Sensor? Is it the small connector on the on the passenger side on the Throttle Body itself that has 6 wires going into the TB?

I disconnected the battery again so hopefully an overnighter will help.

Ugh....

**Jim Lembo** · 07-05-2009, 08:15 PM

Glenn,
Like I told you in our phone conversation earlier today, it can't be nothing else but moisture causing uyour problem. Rocketsled is very knowledgeable and I would have to agree with his diagnosis. Lesson learned: DON'T hose down your engine compartment at the car wash!!!!!!!!!!!!!

When my engine compartment gets dirty, I blow off the dust and crap with compressed air and then use a very mild glass cleaner and a rag to wipe it down,,,,,honestlly, I could care less about what things look like under the hood,,,,,I ain't trying to win any "white glove" car shows!

Jimbo

GR8 WHITE · 07-05-2009, 08:25 PM

Quote:

Originally Posted by Jim Lembo

Glenn,
Like I told you in our phone conversation earlier today, it can't be nothing else but moisture causing uyour problem. Rocketsled is very knowledgeable and I would have to agree with his diagnosis. Lesson learned: DON'T hose down your engine compartment at the car wash!!!!!!!!!!!!!

When my engine compartment gets dirty, I blow off the dust and crap with compressed air and then use a very mild glass cleaner and a rag to wipe it down,,,,,honestlly, I could care less about what things look like under the hood,,,,,I ain't trying to win any "white glove" car shows!

Jimbo

Yeah....I hear ya. I guess just seeing dirt itself annoys me. I never had this problem before so hopefully it isn't something mechanical electrical related.

Will give it an overnighter dry spell. Lets see what happens.

seamus2154 · 07-05-2009, 08:51 PM

Glenn, I had a similar problem two yrs ago on my C5Z. I had just washed down the motor also. Which I had gotten away w/ many times. The difference was I usually start the car after the degreaser but bfr hosing off. Then I while running use compressed air then take it for a run to dry it out. That time I just hosed it started it and then shut it down. Big no no . Water and or steam went where it shouldnt. Then it wouldn't start. Two days later it started ran rough for 5 min then I drove it and dryed it out. No problems after that. High power water is asking for trouble but even the hose can cause problems. If you must start it after the cleaner then hose off lightly and then drive after leaf blower or compressed air. You may get lucky tomorrow...or the next day!! LOl Good luck.

**PerforminNorman** · 07-05-2009, 08:55 PM

I got this Anonymous call from a guy named "Rodney" who left me a voice mail about the exact same issue. He said he lived in Arizona. Glenn, do you know him?

GR8 WHITE · 07-05-2009, 08:59 PM

Quote:

Originally Posted by PerforminNorman

I got this Anonymous call from a guy named "Rodney" who left me a voice mail about the exact same issue. He said he lived in Arizona. Glenn, do you know him?

Yes, good guy. Give him a call sometime.....Even if you prank call and leave some heavy breathing. I am sure he will know it was you calling.

Maybe he will come stand in the parking lot with ya?

**PerforminNorman** · 07-05-2009, 09:08 PM

Quote:

Originally Posted by GR8 WHITE

Yes, good guy. Give him a call sometime.....Even if you prank call and leave some heavy breathing. I am sure he will know it was you calling.

Maybe he will come stand in the parking lot with ya?

Hard to all him back when I don't have his number? He called me anonymously.

RocketSled · 07-06-2009, 10:10 AM

Quote:

Originally Posted by GR8 WHITE

Rocket, if perhaps you are correct, where is this Throttle Position Sensor? Is it the small connector on the on the passenger side on the Throttle Body itself that has 6 wires going into the TB?

If you look at the TB, you'll see it has two attachments on either side of the throttle plate pivot. One is fairly large, it looks like an electric motor, which is in fact exactly what it is. The "Throttle Actuator Control" is a servo motor, which the PCM uses in order to rotate the throttle plate. On the other side is a short black plastic wart, that houses both TP Sensor 1 and TP Sensor 2. You have codes for both sensors, which is an even better indication that the issue is common to both, which would be the case if you got water inside the plastic enclosure. The trusty service manual says this:

The throttle body for the TAC system is similar to a conventional throttle body with some exceptions. One exception is the use of a motor to control the throttle position (TP) instead of a mechanical cable. The other exception is the new design TP sensor. The TP sensor mounts on the side of the throttle body opposite the throttle actuator motor. The TP sensor is actually 2 individual TP sensors within 1 housing. Separate low reference and 5-volt reference circuits are used in order to connect the TP sensors and the TAC module. The TP sensor 1 signal voltage increases at the same time that the throttle opens. The voltage increases, from approximately 1 volt at 0 throttle to above 3.5 volts at 100 percent throttle. TP sensor 2 signal voltage decreases at the same time that the throttle is opened. The voltage increases from approximately 3.8 volts at 0 throttle to below 1 volt at 100 percent throttle.

GR8 WHITE · 07-06-2009, 10:57 AM

Quote:

Originally Posted by RocketSled

If you look at the TB, you'll see it has two attachments on either side of the throttle plate pivot. One is fairly large, it looks like an electric motor, which is in fact exactly what it is. The "Throttle Actuator Control" is a servo motor, which the PCM uses in order to rotate the throttle plate. On the other side is a short black plastic wart, that houses both TP Sensor 1 and TP Sensor 2. You have codes for both sensors, which is an even better indication that the issue is common to both, which would be the case if you got water inside the plastic enclosure. The trusty service manual says this:

The throttle body for the TAC system is similar to a conventional throttle body with some exceptions. One exception is the use of a motor to control the throttle position (TP) instead of a mechanical cable. The other exception is the new design TP sensor. The TP sensor mounts on the side of the throttle body opposite the throttle actuator motor. The TP sensor is actually 2 individual TP sensors within 1 housing. Separate low reference and 5-volt reference circuits are used in order to connect the TP sensors and the TAC module. The TP sensor 1 signal voltage increases at the same time that the throttle opens. The voltage increases, from approximately 1 volt at 0 throttle to above 3.5 volts at 100 percent throttle. TP sensor 2 signal voltage decreases at the same time that the throttle is opened. The voltage increases from approximately 3.8 volts at 0 throttle to below 1 volt at 100 percent throttle.

Car is up and running, going through idle re-learn from an overnight disconnected battery.

If I needed to replace the sensor cable from the passenger side TB over to teh drive side connection, does anyone have a part number to this cable? It has 6 wires in it. From TB to another connector on driver side. It may be old and wires may be weathered as well.

Anyone have the part number?

Thanks Rocket, your knowledge is awesome.

RocketSled · 07-07-2009, 01:15 PM

GR8, I'm betting the problem is resolved. I doubt disconnecting the battery made any difference, I'm more inclined to believe a long, hot "soak" cooked off (all or most of) the water that got in to the sensor. If there's still any issue, I bet it's lessened from before and that after a few more heat cycles the car will be cured.

Next time you power wash your motor, stay away from the TB, or wrap it in a plastic bag or something.

One additional caution - from experience. The Knock Sensors are located in "wells" in the center of the block under the intake manifold. Water can accumulate in those wells and when it does, it rusts and ruins the sensors necessitating their replacement. Unfortunately, the PCM won't necessarily throw a code, it just never detects knock even when the motor pings like crazy. I had this exact issue on my 98 Coupe.

I remember a GM TSB that actually advised the mechanic to run a bead of silicone around the KS opening in the valley cover to act as a "dam" to keep water from getting in. That's for "normal" water incursions. Your hosing off the motor is probably letting a significant amount of water get under the manifold, you might want to break your wash-down habit altogether because of this concern. Otherwise you may end up without knock retard protection.

racingvette · 07-07-2009, 03:13 PM

If water did get into TPS since it is a resistor pot and could get burned spots which will cause weird problems as the PCM relies on TPS to crosscheck TPS angle to APP/TAC ( drive by wire) and MAF output.
If they do not agree the PCM can trip into limp or open loop modes.

A scanner could be used and even with just key on step on gas pedal and what TPS angle and see if there is any dead spots or

With a ohm meter connect to ground and one of the TPS output and hand turn the butterfly.
One TPS pot output starts at zero and goes up in resistance while the other pot side goes high to low.